1. Field of the Invention
The present invention relates to image forming apparatuses.
2. Description of the Related Art
There is known an inkjet type image forming apparatus provided with a liquid droplet jetting head for jetting ink droplets. The inkjet type image forming apparatus forms images by applying ink droplets onto a recording medium while conveying the recording medium.
An “image forming apparatus” means a device for forming images by jetting liquid onto an image recording medium such as paper, threads, fiber, cloth, leather, metal, plastic, glass, wood, and ceramics. “Image forming” does not only mean applying images with meaning such as characters and figures onto an image recording medium, but also means applying images without meaning such as patterns onto an image recording medium (merely jetting liquid onto an image recording medium). Furthermore, “ink” is not limited to so-called ink. Ink is not particularly limited as long as it is a liquid when jet. Ink is used as a collective term of liquids such as a DNA sample, resist, and a pattern material. Furthermore, an “image” is not limited to being applied onto a plane; the image may also be applied onto a three-dimensional object, or the image itself may form a three-dimensional object.
The inkjet type image forming apparatus includes a serial type and a line type. With a serial type image forming apparatus, an image is formed on a sheet while moving the liquid droplet jetting head in a sheet width direction. With a line type image forming apparatus, the liquid droplet jetting head is wider than the width of a sheet that can be conveyed by the device, and an image is formed on the sheet while fixing the liquid droplet jetting head.
An inkjet type image forming apparatus described above includes a maintenance recovery device having a function of maintaining and recovering the performance of the liquid droplet jetting head. The maintenance recovery device has a cap function for capping nozzle surfaces with a cap member having high sealing properties for preventing the ink around the nozzles from thickening and solidifying due to natural, evaporation of the ink. Furthermore, the maintenance recovery device has a suction discharge function for suctioning and discharging ink with the nozzles of the liquid droplet jetting head for recovering from the state where jetting failures occur due to air bubbles generated in the nozzles, to a proper state. Furthermore, the maintenance recovery device has a wiping function for wiping, with a wiper blade, ink that has adhered to the nozzle surfaces, which may cause variations in the flying properties of the ink droplets that are jet from the nozzles.
As described in patent document 1, in a line type device, the maintenance recovery device is provided adjacent to the liquid droplet jetting head. When maintenance/recovery is performed on the liquid droplet jetting head by the maintenance recovery device, first, the liquid droplet jetting head is raised. Next, the maintenance recovery device is moved underneath the liquid droplet jetting head. Then, a predetermined maintenance recovery operation is executed by the maintenance recovery device. When forming an image, the maintenance recovery mechanism is withdrawn, and then the liquid droplet jetting head is lowered to a position where the gap between the liquid droplet jetting head and the sheet is an appropriate size.
In the line type device, it is necessary to precisely stop the liquid droplet jetting head at various positions, such as the position for forming an image onto plain paper, the position for forming an image onto cardboard, a withdraw position for allowing the maintenance recovery device to move underneath the liquid droplet jetting head, the cap position where the nozzle surfaces are caused to contact the caps of the maintenance recovery device, and a wiping position where the wiper blade of the maintenance recovery device is caused to contact the nozzle surfaces.
FIG. 35 illustrates a conventional head elevating mechanism 410 for raising and lowering the liquid droplet jetting head.
As shown in FIG. 35, the head elevating mechanism 410 includes plural feed screws 400 inserted in screw holes provided in a head part 40 and plural detection sensors 401 for detecting the head part 40. By rotating the plural feed screws 400 in synchronization, the head part 40 is raised/lowered. Based on a detection result of detecting the head part 40 obtained by the detection sensors 401, the rotation of the plural feed screws 400 is stopped, and the head part 40 is stopped at a predetermined height.
In the head elevating mechanism 410 shown in FIG. 35, when the rotation of the feed screws 400 is stopped based on the detection result of the detection sensors 401, the feed screws 400 move by the inertia of a driving motor. Therefore, the head part 40 cannot be precisely stopped at the respective positions.
Furthermore, it is necessary to implement control based on the detection result for precisely stopping the driving motor that rotates the feed screws 400. This leads to an increase in the cost of the device.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2011-11498